The PowerScale accelerator nodes do not contain any primary data drives. As such, L1 cache is used differently in the cluster as compared to the traditional storage nodes. Instead, the entire read cache is L1 cache because all the data is fetched from other storage nodes. Also, cache aging is based on a least recently used (LRU) eviction policy, as opposed to the drop-behind algorithm typically used in a storage node’s L1 cache. Because an accelerator’s L1 cache is large and the data in it is much more likely to be requested again, data blocks are not immediately removed from cache upon use. However, metadata and updates of heavy workloads do not benefit as much, and an accelerator’s cache is only beneficial to clients directly connected to the node.
